ansawise - elements of client/server computing · title: ansawise - elements of client\server...

$: ANSAwise - Elements of Client/Server Computing · Title: ANSAwise - Elements of Client\Server Computing Author: Chris Mayers Subject: 04\05\95 Created Date: 2/9/1999 8:22:48 PM$
Copyright 1995 Architecture Projects Management Limited

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APM.1477.01 Approved 4th May 1995

Briefing Note

ANSAwise - Elements of Client/Server Computing

Chris Mayers

Abstract

Organizations may be aware that client/server computing can meet business needs, but beunsure which technology would be meet their needs.

There are many possible techniques and products being sold under the banner of “client/server”.Each has different strengths and weaknesses.

This module of the ANSAwise training programme starts with an general definition of client/server,then explores each technique in turn. The presentation is historical, starting with client/server, andending with intelligent software agents.

Client/Server 1Approved © Copyright 1995 Architecture Projects Management LimitedAPM.1477.01

Elements of Client/Server Computing


In this session

• Examine the ideas behind client/server computing

• Examine the different types of client/server products

• Review the issues that affect large-scale client/server systems


What is client/server computing?

• ‘The splitting of an application into tasks that are performed onseparate computers, one of which is a programmable workstation’

• ‘User control of applications, IT control of infrastructure’

• ‘The marriage of the usability of PCs to the infrastructure of themainframe’

• ‘Distributed data + distributed processing + graphical user interface’

...?


Techniques for client/server computing

• Terminal emulation

• Data download

• Remote data access

• Intelligent agents


Terminal emulation

• In the 1970s, each computer was designed to used a particular typeof terminal

• To use each host system, you had to use a different type of terminal

• So, manufacturers offered terminals that could also emulate othertypes of terminals


Terminal emulation and the PC

• In the 1980s, the terminal emulation could be done by special PCsoftware

• The PC was directly connected to the host computer, just like theoriginal terminal


Terminal emulation and the PC network

• With the rise of the PC local area network (LAN), not every PC neededa host connection

- connection was indirect, via the LAN

• This was done with a communications gateway

- funnelling traffic to the host computer


Beyond terminal emulation

• Terminal emulation is effective, but does not exploit the capabilitiesof the PC

• The user interface looks just as it would on a real terminal

- very different from the PC’s own user interface

• We can fit a PC-style ‘look and feel’ to the terminal emulation

- this is called “screen-scraping”


“Screen Scraping”

• Provides a ‘face-lift’ for terminal emulation

• Usually provides

- short-cut keys for quick access

- access to several host computers or applications at the same time

• May provide

- integration into desktop productivity applications (spreadsheets,...)

- continuous monitoring and display of information

- a single point of login


Screen Scraping - advantages and disadvantages

• Advantages

- low risk

- host computer continues to maintain data integrity

- a technique that is always available

• Disadvantages

- “Brittle” - there can be a high maintenance overhead

- it’s the same original application underneath

- need to support and train users on old and new user interfaces

- there are no open standards for screen scraping


Data Download

• Fetch the data from the host computer (possibly via acommunications gateway)

- download data to individual machines, or a local LAN file server

- download data from more than one source

• Analyse the data with local applications


Data Download - building the local applications

• Use whichever software development tools you prefer

- a standard application package

- a standard database package

- a 4GL

- a graphical development tool


Data Download - advantages and disadvantages

• Advantages

- little change needed to host system

- each data is internally consistent

- flexible information processing

• Disadvantages

- cannot easily be used to update information

- does not cope well with large volumes of data

- relies on understanding the format of the source data


Remote Data Access

• Applications send and receive data directly from the host system

- program-to-program communication, not terminal emulation

• Information processing is cooperative between the client and theserver

- the host system is the server


Remote Data Access - advantages and disadvantages

• Advantages

- most flexibility in developing new applications

- it may be possible to use standard software development tools

• Disadvantages

- local applications become responsible for data consistency

- impractical if the host system does not provide suitable interfaces

- it may place an unacceptable load on the host system


Intelligent Software Agents

• Intelligent agents will move around networks

- gathering and processing information, before returning to the user

• It will be some years before agent technology is mainstream

• It will be used together with other client/server techniques


General Issues for Client/Server Systems

• Scalability- can the system expand as needed?

- can the system be deployed in small and large configurations?

• Interoperability- can the system interwork with other systems?

• Dependability- can the system be made reliable?

- can the system be made secure?

• Internationalization- can the system be deployed anywhere in the world?


What People Say About Client/Server: Facts or Fallacies?

• “By the year 2000 there will be no mainframes”

• “70% of all commercial applications at the enterprise level will beUnix by 1996”

• “UK leads the world in client-server deployment”

• “Only 1 in 4 department client/server applications built today evergets completed”

• “Client/server is more expensive than mainframes”


The Cost of Client/Server• How much does a client/server terminal cost per year?


Client/Server Cost per User

• From a rolling survey of 30 large US organizations

Source: Real Decisions

Support £1700 53.2%

Hardware £870 27.7%

Software £330 10.6%

LAN £270 8.5%


Choice without Order?

• Diverse types of solution elements

- networks

- platforms

- operating systems

• Diverse types of requirements

- for services

- for applications

• ... but who is responsible for the end-to-end solution?


Constructing the end-to-end solution

• We have solution elements...

- ...networks, platforms, operating systems,...

• We have approaches...

- ...open systems, client/server, object-orientation,...

• ...we need a framework for choice


Open architectural framework for solutions

• We need an open architectural framework that

- guides the choices in solution elements and approaches

- protects the investment in networking and legacy systems

- allows integration of products from many vendors

- minimises risk

- supports large-scale client/server systems


Large-scale client/server

• Typically, large-scale client/server systems are distributed systems,rather than centralized ones

- distributed systems being those which consist of interconnectedcooperating components...

- ...there being no central machine (or group of machines)


Interoperability in distributed systems

• Interoperability is difficult to achieve in distributed systems becauseof diversity

- communication protocols, data representations, hardware platforms,...

• “Middleware” is a software infrastructure that facilitatesinteroperability

• So, the open architectural framework must embrace distributedsystems using open middleware technology


Summary

• There is a wide range of techniques in client/server computing

- to support large-scale and small-scale systems

• Different techniques are useful in different circumstances

• For large-scale client/server systems, an architectural framework isneeded

• Client/server will not replace the mainframe for all purposes

ansawise - elements of client/server computing · title: ansawise - elements of client\server...

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